Filtration media possessing high filtration efficiency of small sized particulates generally requires small pores in the media so that the particulates to be filtered cannot pass through the media. Small pores in a media however generally result in low permeability and therefore cause high fluid pressure drop through the media. When particulates are captured physically on the upstream side of the media, they will over time gradually block the pores of the media which in turn cause the fluid pressure drop across the media to gradually increase. The quality of any filtration media is thus characterized by the amount of particulates that are capable of being captured (also known as “media capacity”), which occurs at a specific predetermined pressure drop. If the specific predetermined pressure is reached too rapidly, the resulting media capacity will thus be low. The general rule in the filtration industry is that the higher the efficiency possessed by a filtration media, the lower its capacity. Oftentimes therefore a compromise is needed to achieve both acceptable filtration media efficiency and capacity.
High efficiency filtration media, such as required for fuel filtration, often contain staple glass microfibers. Glass microfibers possess unique filtration properties due to their needle-like fiber shape, rigidity and small size. Glass microfibers are therefore widely used in conventional filtration media to provide both high efficiency and high capacity.
With increasing process pressure, for example during heavy-duty diesel fuel filtration, concerns have risen that glass microfibers could be washed out from the filtration media with the filtered fuel and thus enter and damage the internal combustion engine. In order to prevent problems that could result from glass microfibers leaching out of the filtration media, efforts have been made to develop high-efficiency and high capacity glass-free alternatives to glass microfiber-containing media. The leaching of glass microfibers into the downstream filtrate is not only of concern for internal combustion engine fuel filtration, but also for example in any kind of filtration that comes in contact with the human body, e.g. through ingestion.
Conventional commercially available glass-free filtration media often contain a base-media that provides the required filtration efficiency, e.g. from 100% wood pulp, and a laminated layer of fine staple fibers that provides the required filtration capacity. The manufacture of these conventional forms of filtration media requires high-pressure nipping of the media as well as a multi-stage manufacturing process including the lamination of the efficiency and the capacity layers, resulting in overall high production cost. The multi-layer structure of these conventional media often also results in relatively higher thickness, which is disadvantageous for the pleat geometry of the resulting filter.
It would therefore be highly desirable if filtration media could be provided which is glass-free (i.e., does not contain any glass fibers) but yet exhibits high filtration capacity and efficiency. Such filtration media should also possess a minimum strength sufficient to be further processed and/or pleated (e.g., so as to allow for the formation of filter units comprising such media). It is therefore towards fulfilling such desirable attributes that the present invention is directed.